Organic compounds

ABSTRACT

The present invention relates to certain PDE2 inhibitory compounds, in free or salt form, pharmaceutical compositions containing such compounds and methods for the treatment of PDE2 mediated disorders.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a United States Application under 35 U.S.C. 371 claiming benefit of PCT Application No. PCT/US2015/064331, filed on Dec. 7, 2015, which claims priority to U.S. Provisional Application No. 62/088,540 filed Dec. 6, 2014, the contents of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to PDE2 inhibitory compounds of Formula I as described below, their use as pharmaceuticals and pharmaceutical compositions comprising them. These compounds are useful e.g., in the treatment of PDE2-mediated disorders such as anxiety, depression, autism spectrum disorder (ASD), schizophrenia and cognitive impairment.

BACKGROUND OF THE INVENTION

PDE2 is a 105-KDa homodimer that is expressed in a wide variety of tissues and cell types including brain (including hippocampus, striatum and prefrontal cortex), heart, platelets, endothelial cells, adrenal glomerulosa cells and macrophages. Although cGMP is the preferred substrate and effector molecule for this enzyme, PDE2 hydrolyzes both cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) and is thought to be involved in a number of physiological processes. In particular, it has been shown that inhibition of nitric oxide synthase (NOS), which reduces cGMP signaling, attenuates the behavioral effects of the benzodiazepine chlordiazepoxide, an anxiolytic compound. Also, commercially-available tool inhibitors of PDE2 such as Bay 60-7550 have been shown to increase cyclic nucleotide levels in the brain and have significant anti-anxiety and anti-depressant effects in normal and stressed rodents (Xu et al., Eur. J. Pharmacol. (2005) 518:40-46; Masood et al., J. Pharmacol. Exp. Ther. (2008) 326:369-379; Masood et al., JPET (2009) 331:690-699; Xu et al., Intl. J. Neuropsychopharmacol. (2013) 16:835-847). Inhibition of PDE2 by Bay 60-7550 has also been shown to elevate cGMP and cAMP levels in stimulated primary neuronal cultures in a dose responsive manner; enhance LTP in hippocampal slice preparations in response to electrical stimulation; enhance learning in novel object recognition animal model and a social recognition task in rats; improve acquisition and consolidation phases of novel object memory in age impaired rats; improve performance on object location and recognition tasks when administered after training. Gomez et al., Bioorg. Med. Chem. Lett. (2013) 23:6522-6527. Bay 60-7550 has also been shown to improve cognition and memory function in rats through the enhancement of nNOS activity in the brain. (Domek-Lopacinska et al. (2008) Brain Res. 1216:68-77). Therefore, PDE2 plays an important role in effective behaviors and cognitive function.

In addition to effective behavior and cognitive function, it has been observed that in endothelial cells, PDE2A mRNA and activity are highly induced in response to tumor necrosis factor-α stimulation in vitro. Selective inhibition of PDE2 activity with 9-(6-phenyl-2-oxohex-3-yl)-2-(3,4-dimethoxybenzyl)-purin-6-one (PDP) greatly alters the barrier function of endothelial cells, suggesting that PDE2 is likely to play an important role in regulating fluid and protein integrity of the circulatory system under pathological conditions. Therefore, PDE2 may be a good pharmacological target for sepsis or in more localized inflammatory responses.

In a recent study, PDE2 inhibition has also been shown to elicit pulmonary dilation, prevents pulmonary vascular remodeling and reduces the right ventricular hypertrophy characteristic of pulmonary hypertension, suggesting therapeutic potential of PDE2 inhibition in pulmonary hypertension. Bubb et al., “Inhibition of Phosphodiesterase 2 Augments cGMP and cAMP Signaling to Ameliorate Pulmonary Hypertension”, Circulation, Aug. 5, 2014, p. 496-507, DOI:10.1161/CIRCULATIONAHA. 114.009751.

Despite the promising preclinical data and the identification of PDE2 as a promising drug target, no PDE2 inhibitors are currently known to be under clinical investigation due in part to the poor metabolic stability and brain penetrance of existing PDE2 compounds. There is thus a need for compounds that selectively inhibit PDE2 activity while demonstrate superior biophysical properties.

SUMMARY OF THE INVENTION

The disclosure provides novel compounds having potent and selective PDE2 inhibitory properties with improved orally availability and brain access. Therefore, in the first aspect, the disclosure provides a compound of Formula I:

wherein

-   -   (i) R₁ is C₁₋₄alkyl (e.g., methyl);     -   (ii) R₂ is selected from the group consisting of:         -   H,         -   —OH,         -   halo (e.g., chloro),         -   C₁₋₄alkyl (e.g., methyl),         -   C₁₋₄alkoxy (e.g., methoxy or ethoxy),         -   —N(R_(f))(R_(g)),         -   —C(O)N(R_(h))(R_(i)),         -   —C(O)OR_(j),         -   —CN,         -   C₁₋₄alkylthio (e.g., ethylthio),         -   heteroaryl (e.g., pyrazolyl, e.g., pyrazol-1-yl),         -   heteroC₃₋₇cycloalkyl (e.g., morpholinyl (e.g.,             morpholin-1-yl) or pyrrolidinyl (e.g., pyrrolidin-1-yl)),             and         -   aryloxy (e.g., phenoxy) wherein said aryl is optionally             substituted with one or more halo (e.g., fluoro), for             example 4-fluorophenoxy;     -   (iii) R₃ is H or C₁₋₄alkyl (e.g., methyl);     -   (iv) R_(a), R_(b), R_(c), R_(d) and R_(e) are independently H,         halo (e.g., chloro or fluoro), —O—C₁₋₆alkyl (e.g., propoxy,         butoxy (e.g., n-butoxy, isobutoxy), —OCH₂-cyclopropyl,         —OCH₂-cyclobutyl or —OCH₂-cyclopentyl);     -   (v) R_(f) and R_(g) are independently H, C₁₋₄alkyl (e.g.,         methyl) or heteroaryl (e.g., pyridyl (e.g., pyrid-2-yl));     -   (vi) R_(h) and R_(i) are independently H or C₁₋₄alkyl (e.g.,         ethyl);     -   (vii) R_(j) is H or C₁₋₄alkyl (e.g., ethyl);         in free or salt form.

The disclosure further provides the compound of Formula I as follows:

-   -   1.1 Formula I, wherein R₁ is C₁₋₄alkyl (e.g., methyl);     -   1.2 Formula 1.1, wherein R₁ is methyl;     -   1.3 Formula I, or any of 1.1-1.2, wherein R₂ is selected from         the group consisting of H; —OH; halo (e.g., chloro); C₁₋₄alkyl         (e.g., methyl); C₁₋₄alkoxy (e.g., methoxy or ethoxy);         —N(R_(f))(R_(g)); —C(O)N(R_(h))(R_(i)); —C(O)OR_(j); —CN;         C₁₋₄alkylthio (e.g., ethylthio); heteroaryl (e.g., pyrazolyl,         e.g., pyrazol-1-yl); heteroC₃₋₇cycloalkyl (e.g., morpholinyl         (e.g., morpholin-1-yl) or pyrrolidinyl (e.g., pyrrolidin-1-yl));         and aryloxy (e.g., phenoxy) wherein said aryl is optionally         substituted with one or more halo (e.g., fluoro), for example         4-fluorophenoxy;     -   1.4 Formula I, or any of 1.1-1.2, wherein R₂ is H;     -   1.5 Formula I, or any of 1.1-1.2, wherein R₂ is —OH;     -   1.6 Formula I, or any of 1.1-1.2, wherein R₂ is halo (e.g.,         chloro);     -   1.7 Formula I, or any of 1.1-1.2, wherein R₂ is chloro;     -   1.8 Formula I, or any of 1.1-1.2, wherein R₂ is C₁₋₄alkyl (e.g.,         methyl);     -   1.9 Formula I, or any of 1.1-1.2, wherein R₂ is methyl;     -   1.10 Formula I, or any of 1.1-1.2, wherein R₂ is C₁₋₄alkoxy         (e.g., methoxy or ethyoxy);     -   1.11 Formula I, or any of 1.1-1.2, wherein R₂ is methoxy;     -   1.12 Formula I, or any of 1.1-1.2, wherein R₂ is ethoxy;     -   1.13 Formula I, or any of 1.1-1.2, wherein R₂ is         N(R_(f))(R_(g));     -   1.14 Formula I or 1.13, wherein R_(f) and R_(g) are         independently H, C₁₋₄alkyl (e.g., methyl) or heteroaryl (e.g.,         pyridyl (e.g., pyrid-2-yl));     -   1.15 Formula I or 1.13, wherein R_(f) is H and R_(g) is selected         from H, C₁₋₄alkyl (e.g., methyl) or heteroaryl (e.g., pyridyl         (e.g., pyrid-2-yl));     -   1.16 Formula I or 1.13, wherein R_(f) is H and R_(g) is pyridyl         (e.g., pyrid-2-yl);     -   1.17 Formula I or 1.13, wherein R_(f) is H and R_(g) is         C₁₋₄alkyl (e.g., methyl);     -   1.18 Formula I or 1.13, wherein R_(f) is H and R_(g) is methyl;     -   1.19 Formula I or 1.13, wherein R_(f) and R_(g) are both H;     -   1.20 Formula I or 1.13, wherein R_(f) and R_(g) are both         C₁₋₄alkyl (e.g., methyl);     -   1.21 Formula I or 1.13, wherein R_(f) and R_(g) are both methyl;     -   1.22 Formula I or 1.13, wherein R_(f) is H and R_(g) is         heteroaryl (e.g., pyridyl (e.g., pyrid-2-yl));     -   1.23 Formula I or 1.13, wherein R₂ is —C(O)N(R_(h))(R_(i)),     -   1.24 Formula I or 1.23, wherein R_(h) and R_(i) are         independently H or C₁₋₄alkyl (e.g., ethyl);     -   1.25 Formula I or 1.23, wherein R_(h) is H and R_(i) is H or         C₁₋₄alkyl (e.g., ethyl);     -   1.26 Formula I or 1.23, wherein R_(h) is H and R_(i) is         C₁₋₄alkyl (e.g., ethyl)     -   1.27 Formula I or 1.23, wherein R_(h) is H and R_(i) is ethyl;     -   1.28 Formula I or 1.23, wherein R_(h) and R_(i) are both H;     -   1.29 Formula I, or any of 1.1-1.2, wherein R₂ is —C(O)OR_(j);     -   1.30 Formula I or 1.29, wherein R_(j) is H or C₁₋₄alkyl (e.g.,         ethyl);     -   1.31 Formula I or 1.29, wherein R_(j) is H;     -   1.32 Formula I or 1.29, wherein R_(j) is C₁₋₄alkyl (e.g.,         ethyl);     -   1.33 Formula I or 1.29, wherein R_(j) is ethyl;     -   1.34 Formula I, or any of 1.1-1.2, wherein R₂ is —CN;     -   1.35 Formula I, or any of 1.1-1.2, wherein R₂ is C₁₋₄alkylthio         (e.g., ethylthio);     -   1.36 Formula I, or any of 1.1-1.2, wherein R₂ is ethylthio;     -   1.37 Formula I, or any of 1.1-1.2, wherein R₂ is heteroaryl         (e.g., pyrazolyl, e.g., pyrazol-1-yl);     -   1.38 Formula I, or any of 1.1-1.2, wherein R₂ is pyrazolyl,         e.g., pyrazol-1-yl;     -   1.39 Formula I, or any of 1.1-1.2, wherein R₂ is         heteroC₃₋₇cycloalkyl (e.g., morpholinyl (e.g., morpholin-1-yl)         or pyrrolidinyl (e.g., pyrrolidin-1-yl));     -   1.40 Formula I, or any of 1.1-1.2, wherein R₂ is         heteroC₅₋₆cycloalkyl;     -   1.41 Formula I, or any of 1.1-1.2, wherein R₂ is morpholinyl         (e.g., morpholin-1-yl);     -   1.42 Formula I, or any of 1.1-1.2, wherein R₂ is pyrrolidinyl         (e.g., pyrrolidin-1-yl);     -   1.43 Formula I, or any of 1.1-1.2, wherein R₂ is aryloxy (e.g.,         phenoxy) wherein said aryl is optionally substituted with one or         more halo (e.g., fluoro), for example 4-fluorophenoxy;     -   1.44 Formula I, or any of 1.1-1.2, wherein R₂ is phenoxy wherein         said phenyl is optionally substituted with one or more halo         (e.g., fluoro), for example 4-fluorophenoxy;     -   1.45 Formula I, or any of 1.1-1.2, wherein R₂ is         4-fluorophenoxy;     -   1.46 Formula I or any of 1.1-1.45, wherein R₃ is H or C₁₋₄alkyl         (e.g., methyl);     -   1.47 Formula I or any of 1.1-1.45, wherein R₃ is H;     -   1.48 Formula I or any of 1.1-1.45, wherein R₃ is C₁₋₄alkyl         (e.g., methyl);     -   1.49 Formula I or any of 1.1-1.45, wherein R₃ is methyl;     -   1.50 Formula I or any of 1.1-1.49, wherein R_(a), R_(b), R_(c),         R_(d) and R_(e) are independently H, halo (e.g., chloro or         fluoro), —O—C₁₋₆alkyl (e.g., propoxy, butoxy (e.g., n-butoxy,         isobutoxy), —OCH₂-cyclopropyl, —OCH₂-cyclobutyl or         —OCH₂-cyclopentyl);     -   1.51 Formula I or any of 1.1-1.50, wherein R_(a), R_(b), R_(c),         R_(d) and R_(e) are independently H;     -   1.52 Formula I or any of 1.1-1.51, wherein R_(a), R_(b), R_(c),         R_(d) and R_(e) are independently halo (e.g., chloro or fluoro);     -   1.53 Formula I or any of 1.1-1.51, wherein R_(a), R_(b), R_(c),         R_(d) and R_(e) are independently chloro or fluoro;     -   1.54 Formula I or any of 1.1-1.53, wherein R_(a), R_(b), R_(c),         R_(d) and R_(e) are independently —O—C₁₋₆alkyl (e.g., propoxy,         butoxy (e.g., n-butoxy, isobutoxy), —OCH₂-cyclopropyl,         —OCH₂-cyclobutyl or —OCH₂-cyclopentyl);     -   1.55 Formula I or any of 1.1-1.53, wherein R_(a), R_(b), R_(c),         R_(d) and R_(e) are independently —O—C₃₋₆alkyl;     -   1.56 Formula I or any of 1.1-1.55, wherein R_(b), R_(c) and         R_(e) are all H;     -   1.57 Formula I or any of 1.1-1.56, wherein R_(b), R_(c) and         R_(e) are all H; and R_(a) and R_(d) are independently selected         from H, halo (e.g., chloro or fluoro), —O—C₁₋₆alkyl (e.g.,         propoxy, butoxy (e.g., n-butoxy, isobutoxy), —OCH₂-cyclopropyl,         —OCH₂-cyclobutyl or —OCH₂-cyclopentyl);     -   1.58 Formula I or any of 1.1-1.56, wherein R_(b), R_(c) and         R_(e) are all H; R_(a) is halo (e.g., chloro or fluoro); and         R_(d) is H, halo (e.g., chloro or fluoro) or —O—C₁₋₆alkyl (e.g.,         propoxy, butoxy (e.g., n-butoxy, isobutoxy), —OCH₂-cyclopropyl,         —OCH₂-cyclobutyl or —OCH₂-cyclopentyl);     -   1.59 Formula I or any of 1.1-1.56, wherein R_(b), R_(c) and         R_(e) are all H; R_(a) is halo (e.g., chloro or fluoro); and         R_(d) is H;     -   1.60 Formula I or any of 1.1-1.56, wherein R_(b), R_(c) and         R_(e) are all H; and R_(a) and R_(d) are both halo (e.g., chloro         or fluoro);     -   1.61 Formula I or any of 1.1-1.56, wherein R_(b), R_(c) and         R_(e) are all H; R_(a) and R_(d) are both chloro;     -   1.62 Formula I or any of 1.1-1.56, wherein R_(b), R_(c) and         R_(e) are all H; R_(a) is halo (e.g., chloro or fluoro); and         R_(d) is —O—C₁₋₆alkyl (e.g., propoxy, butoxy (e.g., n-butoxy,         isobutoxy), —OCH₂-cyclopropyl, —OCH₂-cyclobutyl or         —OCH₂-cyclopentyl);     -   1.63 Formula I or any of 1.1-1.56, wherein R_(b), R_(c) and         R_(e) are all H; R_(a) is halo (e.g., chloro or fluoro); and         R_(d) is —O—C₃₋₆alkyl (e.g., propoxy, butoxy (e.g., n-butoxy,         isobutoxy), —OCH₂-cyclopropyl, —OCH₂-cyclobutyl or         —OCH₂-cyclopentyl);     -   1.64 Formula I or any of 1.1-1.56, wherein R_(b), R_(c) and         R_(e) are all H; R_(a) is chloro; and R_(d) is butoxy (e.g.,         n-butoxy, isobutoxy);     -   1.65 Formula I or any of 1.1-1.56, wherein R_(b), R_(c) and         R_(e) are all H; R_(a) is chloro; and R_(d) is n-butoxy;     -   1.66 Formula I or any of 1.1-1.56, wherein R_(b), R_(c) and         R_(e) are all H; R_(a) is halo (e.g., chloro or fluoro); and         R_(d) is —O—C₁₋₆alkyl (e.g., propoxy, butoxy (e.g., n-butoxy,         isobutoxy), —OCH₂-cyclopropyl, —OCH₂-cyclobutyl or         —OCH₂-cyclopentyl);     -   1.67 Formula I or any of 1.1-1.56, wherein R_(a), R_(b), R_(c)         and R_(e) are all H and R_(d) is —O—C₁₋₆alkyl;     -   1.68 any of the preceding formulae, wherein the compound is         Formula I(i):

-   -   1.69 any of the preceding formulae, wherein the compound is         Formula (ii):

-   -   1.70 any of the preceding formulae, wherein the compound is         Formula I(iii):

-   -   1.71 any of the preceding formulae, wherein the compound is         selected from a group consisting of:

-   1-(5-Butoxy-2-fluorophenyl)-8-(4-fluorophenoxy)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one;

-   1-(5-Butoxy-2-fluorophenyl)-8-(dimethylamino)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one;

-   1-(5-Butoxy-2-fluorophenyl)-3-methyl-8-(pyrrolidin-1-yl)-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one;

-   1-(5-Butoxy-2-fluorophenyl)-3-methyl-8-(1H-pyrazol-1-yl)-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one;

-   1-(5-Butoxy-2-fluorophenyl)-3-methyl-8-(pyridin-2-ylamino)-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one;

-   1-(5-Butoxy-2-fluorophenyl)-8-(ethylthio)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one;

-   1-(5-Butoxy-2-fluorophenyl)-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carbonitrile;

-   1-(5-Butoxy-2-fluorophenyl)-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carboxylic     acid;

-   Ethyl     1-(5-butoxy-2-fluorophenyl)-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carboxylate;

-   1-(5-Butoxy-2-fluorophenyl)-N-ethyl-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carboxamide;

-   1-(5-Butoxy-2-fluorophenyl)-3-methyl-4-oxo-3a,4-dihydro-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carboxamide;

-   8-Chloro-1-(2-chloro-5-(cyclopropylmethoxy)phenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one;

-   1-(2,5-Dichlorophenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one;

-   1-(2-Chlorophenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one;

-   1-(2-Chlorophenyl)-3,5-dimethyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one;

-   1-(2,5-Dichlorophenyl)-3,5-dimethyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one;

-   1-(5-Butoxy-2-chlorophenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one;

-   1-(5-Butoxy-2-fluorophenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one;

-   8-Chloro-1-(2,5-dichlorophenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one;

-   1-(5-Butoxy-2-chlorophenyl)-8-chloro-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one;

-   1-(5-Butoxy-2-chlorophenyl)-8-methoxy-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one;     and

-   1-(2-Chloro-5-(cyclobutylmethoxy)phenyl)-8-methoxy-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one;     -   1.72 any of the preceding formulae wherein the compounds inhibit         phosphodiesterase-mediated (e.g., PDE2-mediated) hydrolysis of         cGMP, e.g., with an IC₅₀ of less than 2 μM, more preferably less         than or equal to 250 nM, more preferably less than or equal to         10 nM in a PDE assay, for example, as described in Example 23,         in free or salt form.

In a particular embodiment, the disclosure provides a compound of Formula I(i):

wherein

-   -   (i) R₁ is C₁₋₄alkyl (e.g., methyl);     -   (ii) R₂ is C₁₋₄alkoxy (e.g., methoxy or ethoxy);     -   (iii) R₃ is H;     -   (iv) R_(b), R_(c) and R_(e) are H; R_(a) is halo and R_(d) is         —O—C₁₋₆alkyl (e.g., propoxy, butoxy (e.g., n-butoxy, isobutoxy),         —OCH₂-cyclopropyl, —OCH₂-cyclobutyl or —OCH₂-cyclopentyl);         in free or salt form.

In a particular embodiment, the disclosure provides a compound of Formula I(i) wherein

-   -   (i) R₁ is C₁₋₄alkyl (e.g., methyl);     -   (ii) R₂ is C₁₋₄alkoxy (e.g., methoxy or ethoxy);     -   (iii) R₃ is H;     -   (iv) R_(b), R_(c) and R_(e) are H; R_(a) is halo and R_(d) is         —OCH₂-cyclobutyl;         in free or salt form.

In a second aspect, the disclosure provides a pharmaceutical composition comprising a Compound of the Disclosure, i.e., Compounds of Formula I, I(i), I(ii) or I(iii), or any of formulae 1.1-1.72, in free or pharmaceutically acceptable salt form, in combination or association with a pharmaceutically acceptable diluents or carrier.

The disclosure also provides methods of using the Compounds of the Disclosure for treatment of PDE2-mediated disorders, e.g., disorders as set forth below (especially treatment of anxiety, depression, autism spectrum disorder (ASD), schizophrenia, cognitive impairment). This list is not intended to be exhaustive and may include other diseases and disorders as set forth below.

Therefore, in a third aspect, the disclosure provides a method for the treatment of a PDE2-mediated disorder, comprising administering to a subject in need thereof a therapeutically effective amount of a Compound of the Disclosure disclosed herein, i.e., Compounds of Formula I, I(i), I(ii) or I(iii), or any of formulae 1.1-1.72, in free or pharmaceutically acceptable salt form, or a pharmaceutical composition disclosed herein.

In a further embodiment of the third aspect, the disclosure provides a method for the treatment of the following disorders:

neurological disorders (such as migraine; epilepsy; Alzheimer's disease; Parkinson's disease; brain injury; stroke; cerebrovascular diseases (including cerebral arteriosclerosis, cerebral amyloid angiopathy, hereditary cerebral hemorrhage, and brain hypoxia-ischemia); spinal muscular atrophy; lateral sclerosis; multiple sclerosis;

cognitive disorders (including amnesia, senile dementia, HIV associated dementia, Alzheimer's associated dementia, Huntington's associated dementia, Lewy body dementia, vascular dementia, drug related dementia, delirium, and mild cognitive impairment); and cognitive dysfunction associated with Parkinson's disease and depression;

mental deficiency (including Down syndrome and fragile X syndrome);

sleep disorders (including hypersomnia, circadian rhythm sleep disorder, insomnia, parasomnia, and sleep deprivation);

psychiatric disorders (such as anxiety (including acute stress disorder, generalized anxiety disorder, social anxiety disorder, panic disorder, post-traumatic stress disorder (PTSD), obsessive-compulsive disorder, specific phobia, social phobia, chronic anxiety disorder and obsessive compulsive disorder);

factitious disorder (including acute hallucinatory mania);

impulse control disorders (including pathological gambling, pathological fire-setting, pathological stealing and intermittent explosive disorder);

mood disorders (including bipolar I disorder, bipolar II disorder, mania, mixed affective state, major depression, chronic depression, seasonal depression, psychotic depression and postpartum depression);

psychomotor disorders (extrapyraamidal and movement disorders, e.g., Parkinsonism, Lewy body disease, tremor, drug-induced tremor, drug-induced tardive dyskineisa, L-dopa-induced dyskinesia and restless leg syndrome);

psychotic disorders (including schizophrenia (e.g., continuous or episodic, paranoid, hebephrenic, catatonic, undifferentiated and residual schizophrenic disorders), schizoaffective disorder, schizophreniform, and delusional disorder);

drug dependence (including narcotic dependence, alcoholism, amphetamine dependence, cocaine addiction, nicotine dependence, and drug withdrawal syndrome);

eating disorders (including anorexia, bulimia, binge eating disorder, hyperphagia, and pagophagia);

pediatric psychiatric disorders (including attention deficit disorder, attention deficit/hyperactive disorder, conduct disorder (e.g., tic disorders such as transient, chronic, motor or vocal tic disorders), autism and autism spectrum disorder (ASD));

mental and behavioral disorders due to psychoactive substance use;

cardiovascular disorder (e.g., pulmonary hypertension and pulmonary arterial hypertension); and

pain (e.g., bone and joint pain (osteoarthritis), repetitive motion pain, dental pain, cancer pain, myofascial pain (muscular injury, fibromyalgia), perioperative pain (general surgery, gynecological), chronic pain and neuropathic pain),

in a subject, preferably a mammal, preferably a human, comprising administering to said subject a therapeutically effective amount of a Compound of the Disclosure disclosed herein, i.e., Compounds of Formula I, I(i), I(ii) or I(iii), or any of formulae 1.1-1.72, in free or pharmaceutically acceptable salt form, or a pharmaceutical composition disclosed herein.

In one embodiment, the disease or disorder is selected from a group consisting of anxiety, depression, autism spectrum disorder and schizophrenia, for example anxiety and/or depression in autistic and/or schizophrenic patients. In another embodiment, the disease or disorder is cognitive impairment associated with schizophrenia or dementia.

In the fourth aspect, the disclosure provides a Compound of the Disclosure disclosed herein, i.e., Compounds of Formula I, I(i), I(ii) or I(iii), or any of formulae 1.1-1.72, in free or pharmaceutically acceptable salt form (for use in the manufacture of a medicament) for the treatment of a PDE2-mediated disorder as disclosed herein.

In the fifth aspect, the disclosure provides a pharmaceutical composition comprising a Compound of the Disclosure disclosed herein, i.e., Compounds of Formula I, I(i), I(ii) or I(iii), or any of formulae 1.1-1.72, in free or pharmaceutically acceptable salt form, in combination or association with a pharmaceutically acceptable diluents or carrier, for use in the treatment of a PDE2-mediated disorder as disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates brain cGMP levels in mice following intraperitoneal injection of the compound of Example 22 (3 mg/kg) or BAY 60-7550 (3 mg/kg), a known PDE2 inhibitor. As shown, the compound of Example 22 increases cGMP leels in the striatum of mice after systemic dosing compared to Bay 60-7550.

DETAILED DESCRIPTION OF THE INVENTION

If not otherwise specified or clear from context, the following terms herein have the following meanings:

-   -   (a) “Alkyl” as used herein is a saturated or unsaturated         hydrocarbon moiety, preferably saturated, preferably having one         to six carbon atoms, preferably having one to four carbon atoms,         which may be linear or branched, and may be optionally mono-,         di- or tri-substituted, e.g., with halogen (e.g., chloro or         fluoro), hydroxy, or carboxy.     -   (b) “Aryl” as used herein is a mono or bicyclic aromatic         hydrocarbon, preferably phenyl, optionally substituted, e.g.,         with alkyl (e.g., methyl), halogen (e.g., chloro or fluoro),         haloalkyl (e.g., trifluoromethyl) or hydroxy.     -   (c) “Heteroaryl” as used herein is an aromatic moiety wherein         one or more of the atoms making up the aromatic ring is sulfur         or nitrogen rather than carbon, e.g., pyridyl or thiadiazolyl,         which may be optionally substituted, e.g., with alkyl, halogen,         haloalkyl or hydroxy.

Compounds of the Disclosure, e.g., Compounds of Formula I, I(i), I(ii) or I(iii), e.g., any of formulae 1.1-1.72, may exist in free or salt form, e.g., as acid addition salts. In this specification unless otherwise indicated, language such as “Compounds of the Disclosure” is to be understood as embracing the compounds in any form, for example free or acid addition salt form, or where the compounds contain acidic substituents, in base addition salt form. The Compounds of the Disclosure are intended for use as pharmaceuticals, therefore pharmaceutically acceptable salts are preferred. Salts which are unsuitable for pharmaceutical uses may be useful, for example, for the isolation or purification of free Compounds of the Disclosure or their pharmaceutically acceptable salts, are therefore also included. Compounds of the Disclosure may in some cases also exist in prodrug form. A prodrug form is compound which converts in the body to a Compound of the Disclosure. For example when the Compounds of the Disclosure contain hydroxy or carboxy substituents, these substituents may form physiologically hydrolysable and acceptable esters. As used herein, “physiologically hydrolysable and acceptable ester” means esters of Compounds of the Disclosure which are hydrolysable under physiological conditions to yield acids (in the case of Compounds of the Disclosure which have hydroxy substituents) or alcohols (in the case of Compounds of the Disclosure which have carboxy substituents) which are themselves physiologically tolerable at doses to be administered. Therefore, wherein the Compound of the Disclosure contains a hydroxy group, for example, Compound-OH, the acyl ester prodrug of such compound, i.e., Compound-O—C(O)—C₁₋₄alkyl, can hydrolyze in the body to form physiologically hydrolysable alcohol (Compound-OH) on the one hand and acid on the other (e.g., HOC(O)—C₁₋₄alkyl). Alternatively, wherein the Compound of the Disclosure contains a carboxylic acid, for example, Compound-C(O)OH, the acid ester prodrug of such compound, Compound-C(O)O—C₁₋₄alkyl can hydrolyze to form Compound-C(O)OH and HO—C₁₋₄alkyl. As will be appreciated, the term thus embraces conventional pharmaceutical prodrug forms.

The Compounds of the Disclosure herein include their enantiomers, diastereoisomers and racemates, as well as their polymorphs, hydrates, solvates and complexes. Some individual compounds within the scope of this invention may contain double bonds. Representations of double bonds in this invention are meant to include both the E and the Z isomer of the double bond. In addition, some compounds within the scope of this invention may contain one or more asymmetric centers. This invention includes the use of any of the optically pure stereoisomers as well as any combination of stereoisomers.

It is also intended that the Compounds of the Disclosure encompass their stable and unstable isotopes. Stable isotopes are nonradioactive isotopes which contain one additional neutron compared to the abundant nuclides of the same species (i.e., element). It is expected that the activity of compounds comprising such isotopes would be retained, and such compound would also have utility for measuring pharmacokinetics of the non-isotopic analogs. For example, the hydrogen atom at a certain position on the Compounds of the Disclosure may be replaced with deuterium (a stable isotope which is non-radioactive). Examples of known stable isotopes include, but not limited to, deuterium, ¹³C, ¹⁵N, ¹⁸O. Alternatively, unstable isotopes, which are radioactive isotopes which contain additional neutrons compared to the abundant nuclides of the same species (i.e., element), e.g., ¹²³I, ¹³¹I, ¹²⁵I, ¹¹C, ¹⁸F, may replace the corresponding abundant species of I, C and F. Another example of useful isotope of the compound of the invention is the ¹¹C isotope. These radio isotopes are useful for radio-imaging and/or pharmacokinetic studies of the compounds of the invention. Isotopically-labeled compounds of Formula I may generally be prepared by carrying out by substituting an isotopically-labeled reagent for a non-isotopically-labeled reagent.

The phrase “Compounds of the Disclosure” or “PDE 2 inhibitors of the Disclosure” encompasses any and all of the compounds disclosed herewith, e.g., a Compound of Formula I, I(i), I(ii), I(iii) or any of 1.1-1.72 as hereinbefore described, in free or salt form.

The words “treatment” and “treating” are to be understood accordingly as embracing treatment or amelioration of symptoms of the disease as well as treatment of the cause of the disease. In one embodiment, the invention provides a method for the treatment of the disease or disorder disclosed herein. In another embodiment, the invention provides a method for the prophylaxis of a disease or disorder as disclosed herein.

For methods of treatment, the word “effective amount” is intended to encompass a therapeutically effective amount to treat a specific disease or disorder.

The term “pulmonary hypertension” is intended to encompass pulmonary arterial hypertension.

The term “subject” includes human or non-human (i.e., animal). In particular embodiment, the invention encompasses both human and nonhuman. In another embodiment, the invention encompasses nonhuman. In other embodiment, the term encompasses human.

The term “comprising” as used in this disclosure is intended to be open-ended and does not exclude additional, unrecited elements or method steps.

The term “cognitive disorders” refers to any disorder comprising a symptom of cognitive deficiency (i.e., subnormal or suboptimal functioning in one or more cognitive aspects such as memory, intellect, learning, logic, attention or executive function (working memory) in an individual compared to other individuals within the same general age population). Therefore, cognitive disorders include but are not limited to amnesia, senile dementia, HIV associated dementia, Alzheimer's associated dementia, Huntington's associated dementia, Lewy body dementia, vascular dementia, drug related dementia, delirium, and mild cognitive impairment. Cognitive disorders can also be a disorder primarily but not exclusively related to psychosis (schizophrenia), mood disorders, bipolar disorders, stroke, frontotemporal dementia, progressive supranuclear palsy, cerebral trauma and drug abuse, Asperger's syndrome and age-associated memory impairment.

Compounds of the Disclosure, e.g., Compounds of Formula I, I(i), I(ii) or I(iii), e.g., any of formulae 1.1-1.72, as hereinbefore described, in free or pharmaceutically acceptable salt form may be used as a sole therapeutic agent, but may also be used in combination or for co-administration with other active agents.

Dosages employed in practicing the present invention will of course vary depending, e.g. on the particular disease or condition to be treated, the particular Compound of the Disclosure used, the mode of administration, and the therapy desired. Compounds of the Disclosure may be administered by any suitable route, including orally, parenterally, transdermally, or by inhalation, but are preferably administered orally. In general, satisfactory results, e.g. for the treatment of diseases as hereinbefore set forth are indicated to be obtained on oral administration at dosages of the order from about 0.01 to 2.0 mg/kg. In larger mammals, for example humans, an indicated daily dosage for oral administration will accordingly be in the range of from about 0.75 to 150 mg, conveniently administered once, or in divided doses 2 to 4 times, daily or in sustained release form. Unit dosage forms for oral administration thus for example may comprise from about 0.2 to 75 or 150 mg, e.g. from about 0.2 or 2.0 to 50, 75 or 100 mg of a Compound of the Disclosure, together with a pharmaceutically acceptable diluent or carrier therefor.

Pharmaceutical compositions comprising Compounds of the Disclosure may be prepared using conventional diluents or excipients and techniques known in the galenic art. The pharmaceutically acceptable carrier may comprise any conventional pharmaceutical carrier or excipient. Suitable pharmaceutical carriers include inert diluents or fillers, water and various organic solvents (such as hydrates and solvates). The pharmaceutical compositions may, if desired, contain additional ingredients such as flavorings, binders, excipients and the like. Thus for oral administration, tablets containing various excipients, such as citric acid, may be employed together with various disintegrants such as starch, alginic acid and certain complex silicates and with binding agents such as sucrose, gelatin and acacia. Additionally, lubricating agents such as magnesium stearate, sodium lauryl sulfate and talc are often useful for tableting purposes. Solid compositions of a similar type may also be employed in soft and hard filled gelatin capsules. Non-limiting examples of materials, therefore, include lactose or milk sugar and high molecular weight polyethylene glycols. When aqueous suspensions or elixirs are desired for oral administration the active compound therein may be combined with various sweetening or flavoring agents, coloring matters or dyes and, if desired, emulsifying agents or suspending agents, together with diluents such as water, ethanol, propylene glycol, glycerin, or combinations thereof. The pharmaceutical composition may, for example, be in a form suitable for oral administration as a tablet, capsule, pill, powder, sustained release formulation, solution or suspension, for parenteral injection as a sterile solution, suspension or emulsion, for topical administration as an ointment or cream or for rectal administration as a suppository.

The compounds of the Disclosure herein and their pharmaceutically acceptable salts may be made using the methods as described and exemplified herein and by methods similar thereto and by methods known in the chemical art. Such methods include, but not limited to, those described below. If not commercially available, starting materials for these processes may be made by procedures, which are selected from the chemical art using techniques which are similar or analogous to the synthesis of known compounds. All references cited herein are hereby incorporated by reference in their entirety.

EXAMPLE 1 1-(5-Butoxy-2-fluorophenyl)-8-(4-fluorophenoxy)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one

(a) 5-Butoxy-2-fluorobenzenamine

A mixture of 4-fluoro-3-nitrophenol (1) (2.81 g, 17.9 mmol), 1-bromobutane (3.43 g, 25.0 mmol) and cesium carbonate (11.6 g, 35.7 mmol) in anhydrous DMF (15 mL) is stirred at room temperature for 18 h. After the solvent is removed under reduced pressure, the residue is treated with water (400 mL) and extracted with methylene (3×50 mL). The combined organic phase is evaporated to dryness to give 4-butoxy-1-fluoro-2-nitrobenzene as an orange oil. To a solution of the crude 4-butoxy-1-fluoro-2-nitrobenzene in EtOH (10 mL) is slowly added concentrated HCl (10 mL). The mixture is stirred at room temperature for 5 min, and then tin(II) chloride (8.40 g, 44.3 mmol) is added. After stirring at room temperature for 16 h, the reaction mixture is treated with water (500 mL) and extracted with methylene (4×50 mL). The combined organic phase is washed with brine (40 mL), and then evaporated to dryness under reduced pressure. The obtained crude product is further purified with a neutral alumina oxide column using a gradient of 0-100% ethyl acetate in hexane as eluent to give 5-butoxy-2-fluorobenzenamine an oil (2.42 g, 74% yield). MS (ESI) m/z 184.1 [M+H]⁺.

(b) (5-Butoxy-2-fluorophenyl)hydrazine

A solution of sodium nitrite (1.04 g, 15.1 mmol) in water (5 mL) is added dropwise to a suspension of 5-butoxy-2-fluorobenzenamine (2.30 g, 12.6 mmol) in concentrated hydrochloric acid (12 mL) at 0° C. After the completion of the addition, the reaction mixture is stirred at 0° C. for 30 min, and then a solution of tin (II) chloride dihydrate (6.86 g, 30.4 mmol) in concentrated hydrochloric acid (3 mL) is added. The reaction mixture is stirred at room temperature overnight, and then filtered. The filter cake is washed with 6 N HCl (3×4 mL) and hexane (3×5 mL) successively, and then dried under vacuum to give 3.18 g of the crude product, which is used directly in the next step without further purification. MS (ESI) m/z 199.1 [M+H]⁺.

(c) 8-Bromo/Chloro-1-(5-butoxy-2-fluorophenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one

To a suspension of (4-butoxy-2-fluorophenyl)hydrazine (860 mg, 4.34 mmol) and 3-acetyl-6-bromo-4-hydroxy-1,5-naphthyridin-2(1H)-one (500 mg, 1.77 mmol) in dioxane (4 mL) is added concentrated HCl (0.1 mL). The reaction mixture in a sealed tube is stirred at room temperature for 5 min and then heated in a microwave reactor at 160° C. for 5 h. After cooled to room temperature, the reaction mixture is treated with water (200 mL) and then extracted with CH₂Cl₂/MeOH (10/1) (4×50 mL). The combined organic phase is evaporated to dryness. The obtained residue is purified by silica-gel column chromatography using a gradient of 0-100% ethyl acetate in hexane as eluent to give 580 mg of product, which contains 22% of 8-chloro-1-(5-butoxy-2-fluorophenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one (MS (ESI) m/z 401.1 [M+H]⁺) and 68% 8-bromo-1-(5-butoxy-2-fluorophenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one (MS (ESI) m/z 445.1 [M+H]⁺). The two compounds co-eluted on the column and are used directly in the next step without further separation.

(d) 1-(5-Butoxy-2-fluorophenyl)-8-(4-fluorophenoxy)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one

A suspension of 8-bromo/chloro-1-(5-butoxy-2-fluorophenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one (41.0 mg), 4-fluorophenol (112 mg, 1.00 mmol) and cesium carbonate (97 mg, 0.30 mmol) in dioxane (0.6 mL) in a sealed microwave vial is heated in a microwave reactor at 160° C. for 5 h. After cooled to room temperature, the reaction mixture is treated with water (100 mL) and extracted with CH₂Cl₂ (4×25 mL). The combined organic phase is evaporated to dryness. The obtained residue is purified with a semi-preparative HPLC system using a gradient of 0-70% acetonitrile in water containing 0.1% formic acid over 16 min to give 17 mg of 1-(5-butoxy-2-fluorophenyl)-8-(4-fluorophenoxy)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one as an off-white solid. ¹H NMR (500 MHz, Chloroform-d) δ 11.24 (s, 1H), 7.81 (d, J=8.9 Hz, 1H), 7.13 (d, J=8.8 Hz, 1H), 6.88 (dd, J=6.0, 3.1 Hz, 1H), 6.85-6.78 (m, 4H), 6.76-6.70 (m, 1H), 6.62 (dd, J=9.2, 9.2 Hz, 1H), 4.03-3.78 (m, 2H), 2.79 (s, 3H), 1.81-1.74 (m, 2H), 1.58-1.45 (m, 2H), 1.00 (t, J=7.4 Hz, 3H). MS (ESI) m/z 477.2 [M+H]⁺.

EXAMPLE 2 1-(5-Butoxy-2-fluorophenyl)-8-(dimethylamino)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one

The title compound is prepared in an analogous fashion following the procedure described in the synthesis of Example 1 wherein 40% dimethylamine solution is added in step (d) instead of 4-fluorophenol. ¹H NMR (500 MHz, Chloroform-d) δ 10.82 (s, 1H), 7.56 (d, J=9.1 Hz, 1H), 7.15-7.08 (m, 2H), 6.99-6.92 (m, 1H), 6.80 (d, J=9.0 Hz, 1H), 3.97 (t, J=6.5 Hz, 2H), 2.81 (s, 3H), 2.77 (s, 6H), 1.81-1.71 (m, 2H), 1.53-1.42 (m, 2H), 0.96 (t, J=7.4 Hz, 3H). MS (ESI) m/z 410.2 [M+H]⁺.

EXAMPLE 3 1-(5-Butoxy-2-fluorophenyl)-3-methyl-8-(pyrrolidin-1-yl)-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one

The title compound is prepared in an analogous fashion following the procedure described in the synthesis of Example 1 wherein pyrrolidine is added in step (d) instead of 4-fluorophenol. ¹H NMR (500 MHz, Chloroform-d) δ 10.28 (s, 1H), 7.47 (d, J=9.0 Hz, 1H), 7.15-7.08 (m, 2H), 7.00-6.92 (m, 1H), 6.55 (d, J=9.0 Hz, 1H), 3.97 (t, J=6.5 Hz, 2H), 3.16-3.01 (m, 4H), 2.80 (s, 3H), 1.95-1.84 (m, 4H), 1.80-1.71 (m, 2H), 1.53-1.43 (m, 2H), 0.96 (t, J=7.4, 7.4 Hz, 3H). MS (ESI) m/z 436.2 [M+H]⁺.

EXAMPLE 4 1-(5-Butoxy-2-fluorophenyl)-3-methyl-8-(1H-pyrazol-1-yl)-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one

The title compound is prepared in an analogous fashion following the procedure described in the synthesis of Example 1 wherein 1H-pyrazole is added in step (d) instead of 4-fluorophenol. ¹H NMR (500 MHz, Chloroform-d) δ 10.83 (s, 1H), 8.15 (d, J=8.9 Hz, 1H), 7.83 (d, J=8.9 Hz, 1H), 7.67 (dd, J=1.7, 0.8 Hz, 1H), 7.59 (dd, J=2.6, 0.8 Hz, 1H), 7.25-7.16 (m, 2H), 7.14-7.08 (m, 1H), 6.33 (dd, J=2.6, 1.6 Hz, 1H), 4.00 (t, J=6.5 Hz, 2H), 2.84 (s, 3H), 1.82-1.72 (m, 2H), 1.53-1.43 (m, 2H), 0.96 (t, J=7.4 Hz, 3H). MS (ESI) m/z 433.2 [M+H]⁺.

EXAMPLE 5 1-(5-Butoxy-2-fluorophenyl)-3-methyl-8-(pyridin-2-ylamino)-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one

A suspension of the crude 8-bromo/chloro-1-(5-butoxy-2-fluorophenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one synthesized in step c of Example 1 (41.0 mg), pyridin-2-amine (160 mg, 1.7 mmol), Pd₂(dba)₃ (8 mg), Xantphos (10 mg) and cesium carbonate (130 mg, 0.40 mmol) in dioxane (0.6 mL) is heated in at 100° C. for 60 h. After cooled to room temperature, the reaction mixture is treated with DMF (5 mL) and then filtered. The filtrate is isolated with a semi-preparative HPLC system using a gradient of 0-30% acetonitrile in water containing 0.1% formic acid over 16 min to give 11 mg of 1-(5-butoxy-2-fluorophenyl)-3-methyl-8-(pyridin-2-ylamino)-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one as an off-white solid. ¹H NMR (500 MHz, DMSO-d₆) δ 11.43 (s, 1H), 9.67 (s, 1H), 8.16-8.09 (m, 1H), 7.68 (d, J=9.0 Hz, 1H), 7.38-7.32 (m, 1H), 7.32-7.27 (m, 2H), 7.19-7.10 (m, 2H), 6.98-6.91 (m, 1H), 6.83-6.76 (m, 1H), 3.99 (t, J=6.4 Hz, 2H), 2.60 (s, 3H), 1.71-1.60 (m, 2H), 1.45-1.31 (m, 2H), 0.87 (t, J=7.4 Hz, 3H). MS (ESI) m/z 459.2 [M+H]⁺.

EXAMPLE 6 1-(5-Butoxy-2-fluorophenyl)-8-(ethylthio)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one

The title compound is prepared in an analogous fashion following the procedure described in the synthesis of Example 1 wherein ethanethiol is added in step (d) instead of 4-fluorophenol. ¹H NMR (500 MHz, Chloroform-d) δ 11.00 (s, 1H), 7.56 (d, J=8.7 Hz, 1H), 7.24 (d, J=8.7 Hz, 1H), 7.18-7.09 (m, 2H), 7.03-6.98 (m, 1H), 3.97 (t, J=6.4 Hz, 2H), 2.81 (s, 3H), 2.51 (q, J=7.4 Hz, 2H), 1.81-1.73 (m, 2H), 1.53-1.44 (m, 2H), 1.01 (t, J=7.4 Hz, 3H), 0.97 (t, J=7.4 Hz, 3H). MS (ESI) m/z 427.2 [M+H]⁺.

EXAMPLE 7 1-(5-Butoxy-2-fluorophenyl)-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carbonitrile

A suspension of the crude 8-bromo/chloro-1-(5-butoxy-2-fluorophenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one prepared in step c of Example 1 (140 mg) and copper(I) cyanide (50 mg, 0.56 mmol) in pyridine (1.5 mL) in a seal microwave vial is heated in a microwave reactor at 180° C. for 5 h. After cooled to room temperature, the solvent is removed under reduced pressure. The residue is treated with ethyl acetate (15 mL), and then filtered. The filtrate is washed with water three times (3×5 mL), and then evaporated to dryness. The obtained crude product is purified by silica gel column chromatography to give 71 mg of 1-(5-butoxy-2-fluorophenyl)-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carbonitrile as an off white solid. ¹H NMR (500 MHz, Chloroform-d) δ 11.23 (s, 1H), 7.80 (d, J=8.5 Hz, 1H), 7.73 (d, J=8.2 Hz, 1H), 7.23-7.15 (m, 1H), 7.13-7.08 (m, 1H), 7.08-7.01 (m, 1H), 4.00 (t, J=6.5 Hz, 2H), 2.82 (s, 3H), 1.84-1.74 (m, 2H), 1.53-1.47 (m, 2H), 0.98 (t, J=7.4 Hz, 3H). MS (ESI) m/z 392.1 [M+H]⁺.

EXAMPLE 8 1-(5-Butoxy-2-fluorophenyl)-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carboxylic acid

To a suspension of 1-(5-butoxy-2-fluorophenyl)-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carbonitrile (56 mg, 0.14 mmol) in dioxane (1.0 mL) is added concentrated hydrochloric acid (0.15 mL). The reaction mixture is stirred at 100° C. for 24 h. After the solvents are removed under reduced pressure, the residue is further dried under vacuum to afford 1-(5-butoxy-2-fluorophenyl)-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carboxylic acid (45 mg, 77% yield) as an off white solid. ¹H NMR (500 MHz, Chloroform-d) δ 10.87 (s, 1H), 9.49 (s, 1H), 8.30 (d, J=8.1 Hz, 1H), 7.90 (d, J=8.4 Hz, 1H), 7.30-7.23 (m, 1H), 7.19-7.15 (m, 1H), 7.14-7.08 (m, 1H), 4.12-3.92 (m, 2H), 2.84 (s, 3H), 1.86-1.74 (m, 2H), 1.53-1.45 (m, 2H), 0.98 (t, J=7.4, 7.4 Hz, 3H). MS (ESI) m/z 411.1 [M+H]⁺.

EXAMPLE 9 Ethyl 1-(5-butoxy-2-fluorophenyl)-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carboxylate

A mixture of 1-(5-butoxy-2-fluorophenyl)-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carboxylic acid (20 mg, 0.049 mmol) and concentrated sulfuric acid (10 μL) in ethanol (0.60 mL) in a sealed microwave vial is heated in a microwave reactor at 120° C. for 1 h. After cooled to room temperature, the reaction mixture is concentrated under reduced pressure. The obtained residue is purified with a semi-preparative HPLC to give ethyl 1-(5-butoxy-2-fluorophenyl)-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carboxylate (17 mg, 77% yield) as an off white solid. ¹H NMR (500 MHz, Chloroform-d) δ 11.07 (s, 1H), 8.23 (d, J=8.6 Hz, 1H), 7.79 (d, J=8.6 Hz, 1H), 7.19-7.13 (m, 2H), 7.07-7.00 (m, 1H), 4.35-4.24 (m, 2H), 3.99 (t, J=6.5 Hz, 2H), 2.83 (s, 3H), 1.82-1.72 (m, 2H), 1.56-1.42 (m, 2H), 1.30 (t, J=7.2 Hz, 3H), 0.97 (t, J=7.4 Hz, 3H). MS (ESI) m/z 439.2 [M+H]⁺.

EXAMPLE 10 1-(5-Butoxy-2-fluorophenyl)-N-ethyl-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carboxamide

(a) 1-(5-Butoxy-2-fluorophenyl)-4-chloro-N-ethyl-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carboxamide

To a solution of 1-(5-butoxy-2-fluorophenyl)-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carboxylic acid (25 mg, 0.061 mmol) in CH₂Cl₂ (0.75 mL) is added thionyl chloride (45 μL, 0.62 mmol), followed by two drops of DMF. After stirring at 46° C. overnight, the reaction mixture is evaporated to dryness under reduced pressure. The residue is dissolved in CH₂Cl₂ (0.80 mL), and then ethanamine is bubbled through the solution at room temperature for 30 min. After the solvent is removed under reduced pressure, the residue is washed with water twice times (2×1 mL), and then dried under vacuum to give 26 mg of crude 1-(5-butoxy-2-fluorophenyl)-4-chloro-N-ethyl-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carboxamide, which is used in the next step without further purification. MS (ESI) m/z 456.2 [M+H]⁺.

(b) 1-(5-Butoxy-2-fluorophenyl)-N-ethyl-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carboxamide

A suspension of 1-(5-butoxy-2-fluorophenyl)-4-chloro-N-ethyl-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carboxamide (26 mg, 0.057 mmol) and concentrated hydrochloric acid (10 μL) in dioxane (0.50 mL) in a sealed vial is heated in a microwave reactor at 130° C. for 1 h. After cooled to room temperature, the mixture is evaporated to dryness under reduced pressure. The obtained crude product is purified with a semi-preparative HPLC to give 1-(5-butoxy-2-fluorophenyl)-N-ethyl-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carboxamide (11 mg, 44% yield) as a pale yellow solid. ¹H NMR (500 MHz, Chloroform-d) δ 10.77 (s, 1H), 8.30 (d, J=8.5 Hz, 1H), 7.81 (d, J=8.6 Hz, 1H), 7.26-7.16 (m, 2H), 7.13-7.06 (m, 1H), 6.84-6.76 (m, 1H), 4.10-3.90 (m, 2H), 3.42-3.24 (m, 2H), 2.83 (s, 3H), 1.87-1.72 (m, 2H), 1.55-1.42 (m, 2H), 1.11 (t, J=7.3 Hz, 3H), 0.97 (t, J=7.4 Hz, 3H). MS (ESI) m/z 438.2 [M+H]⁺.

EXAMPLE 11 1-(5-Butoxy-2-fluorophenyl)-3-methyl-4-oxo-3a,4-dihydro-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carboxamide

To a suspension of 1-(5-butoxy-2-fluorophenyl)-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carbonitrile (10 mg, 0.026 mmol) in dioxane (0.2 mL) is added 6N NaOH aqueous solution (40 μL). The reaction mixture is heated at 100° C. for 2 h. After cooled to room temperature, the reaction mixture is evaporated to dryness under reduced pressure. The residue is purified with a semi-preparative HPLC system to give 1-(5-butoxy-2-fluorophenyl)-3-methyl-4-oxo-3a,4-dihydro-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carboxamide (3.2 mg, 30% yield) as an off white solid. ¹H NMR (500 MHz, Chloroform-d) δ 10.13 (s, 1H), 8.29 (d, J=8.4 Hz, 1H), 7.76 (d, J=8.3 Hz, 1H), 7.25-7.14 (m, 2H), 7.10-7.02 (m, 1H), 6.59 (s, 1H), 5.32 (s, 1H), 3.99 (t, J=6.5 Hz, 2H), 2.81 (s, 3H), 1.82-1.74 (m, 2H), 1.52-1.46 (m, 2H), 0.97 (t, J=7.4, 7.4 Hz, 3H). MS (ESI) m/z 410.2 [M+H]⁺.

EXAMPLE 12 8-Chloro-1-(2-chloro-5-(cyclopropylmethoxy)phenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one

(a) 5-(Benzyloxy)-2-chlorobenzenamine

A mixture of 4-chloro-5-nitrophenol (2.25 g, 13.0 mmol), (bromomethyl)benzene (2.33 g, 13.6 mmol) and cesium carbonate (8.50 g, 25.9 mmol) in anhydrous N,N-Dimethylacetamide (10 mL) is stirred at room temperature for 2 h. After the solvent is removed under reduced pressure, the residue is treated with water (300 mL) and then extracted with methylene three times (3×30 mL). The combined organic phase is evaporated to dryness to give 4-(benzyloxy)-1-chloro-2-nitrobenzene as an oil. To a solution of the crude 4-(benzyloxy)-1-chloro-2-nitrobenzene in EtOH (10 mL) is slowly added concentrated HCl (8 mL). The mixture is stirred at room temperature for 5 min, and then tin(II) chloride (8.0 g, 42.0 mmol) is added. After stirring at room temperature for 0.5 h, the reaction mixture is treated with water (400 mL) and then extracted with methylene (4×30 mL). The combined organic phase is washed with saturated NaHCO₃ (30 mL) and brine (30 mL) successively, and then evaporated to dryness to give 3.0 g of 5-(benzyloxy)-2-chlorobenzenamine as light orange solid. MS (ESI) m/z 234.1 [M+H]⁺.

(b) (5-(Benzyloxy)-2-chlorophenyl)hydrazine

A solution of sodium nitrite (226 mg, 3.28 mmol) in water (3 mL) is added dropwise to a suspension of 5-(benzyloxy)-2-chlorobenzenamine (640 mg, 2.74 mmol) in concentrated hydrochloric acid (5 mL) at 0° C. After the completion of the addition, the reaction mixture is stirred at 0° C. for 30 min. A solution of tin (II) chloride (2.08 g, 11.0 mmol) in concentrated hydrochloric acid (3 mL) is added. The resulting suspension is stirred at room temperature for 2 h, and then filtered. The filter cake is collected. The filtrate is basified to pH 10 with 10 N NaOH, and then extracted with CH₂Cl₂ (3×40 mL). The combined organic phase is evaporated to dryness. The obtained residue and the collected filter cake are combined and purified with a neutral aluminum oxide column using a gradient of 0-20% methanol in ethyl acetate to give (5-(benzyloxy)-2-chlorophenyl)hydrazine (300 mg, 44% yield). MS (ESI) m/z 249.1 [M+H]⁺.

(c) 8-Chloro-1-(2-chloro-5-hydroxyphenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one

To a suspension of (5-(benzyloxy)-2-fluorophenyl)hydrazine (650 mg, 2.6 mmol) and 3-acetyl-6-bromo-4-hydroxy-1,5-naphthyridin-2(1H)-one (200 mg, 0.71 mmol) in dioxane (2 mL) is added concentrated HCl (0.1 mL). The reaction mixture in a sealed tube is stirred at room temperature for 5 min and then heated at 110° C. for 2 days. After cooling to room temperature, the reaction mixture us treated with water (200 mL) and then extracted with CH₂Cl₂/MeOH (10/1) (4×50 mL). The combined organic phase is evaporated to dryness to give 409 mg of crude 8-chloro-1-(2-chloro-5-hydroxyphenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one, which is used directly in next step without further purification. A small amount of the crude product is purified with a semi-preparative HPLC for structural verification. ¹H NMR (500 MHz, DMSO-d₆) δ 11.70 (s, 1H), 10.13 (s, 1H), 7.77 (d, J=8.7 Hz, 1H), 7.54 (d, J=8.7 Hz, 1H), 7.47-7.41 (m, 1H), 7.02-6.95 (m, 2H), 2.60 (s, 3H). MS (ESI) m/z 361.0 [M+H]⁺.

(d) 8-Chloro-1-(2-chloro-5-(cyclopropylmethoxy)phenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one

A suspension of 8-chloro-1-(2-chloro-5-hydroxyphenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one (60 mg, 0.17 mmol), (bromomethyl)cyclopropane (30 μL, 0.27 mmol) and sodium carbonate (36 mg, 0.23 mmol) in DMF (1.2 mL) in a sealed reaction vial is heated at 100° C. for 2 days. After cooled to room temperature, the reaction mixture is filtered. The filtrate is separated with a semi-preparative HPLC system using a gradient of 0-63% acetonitrile in water containing 0.1% formic acid over 16 min to give 8-chloro-1-(2-chloro-5-(cyclopropylmethoxy)phenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one as an off-white solid (7 mg, 10% yield). ¹H NMR (500 MHz, Chloroform-d) δ 11.08 (s, 1H), 7.71 (d, J=8.6 Hz, 1H), 7.46 (d, J=8.6 Hz, 1H), 7.38 (d, J=8.6 Hz, 1H), 7.14-7.06 (m, 2H), 3.86 (dd, J=7.0, 2.8 Hz, 2H), 2.83 (s, 3H), 1.37-1.24 (m, 1H), 0.73-0.62 (m, 2H), 0.44-0.29 (m, 2H). MS (ESI) m/z 415.1 [M+H]⁺.

EXAMPLE 13 1-(2,5-Dichlorophenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one

To a suspension of 2,5-dichlorophenylhydrazine (80 mg, 0.45 mmol) and 3-acetyl-4-hydroxy-1,5-naphthyridin-2(1H)-one (62 mg, 0.30 mmol) in ethanol (2 mL) is added concentrated HCl (0.1 mL). The reaction mixture in a sealed tube is heated in a microwave reactor at 160° C. for 5 h. After cooled to room temperature, the reaction mixture is diluted with DMF (10 mL) and then filtered. The filtrate is isolated with a semi-preparative HPLC system to give 1-(2,5-Dichlorophenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one (20 mg, 50% yield). ¹H NMR (500 MHz, Chloroform-d) δ 9.95 (s, 1H), 8.27 (dd, J=4.5, 1.4 Hz, 1H), 7.66-7.56 (m, 2H), 7.52-7.43 (m, 2H), 7.37 (dd, J=8.3, 4.5 Hz, 1H), 2.81 (s, 3H). MS (ESI) m/z 345.0 [M+H]⁺.

EXAMPLE 14 1-(2-Chlorophenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one

The title compound is prepared in an analogous fashion following the procedure described in the synthesis of Example 13 wherein (2-chlorophenyl)hydrazine is added instead of 2,5-dichlorophenylhydrazine. ¹H NMR (500 MHz, Chloroform-d) δ 10.22 (s, 1H), 8.24 (dd, J=4.5, 1.4 Hz, 1H), 7.64 (dd, J=8.3, 1.4 Hz, 1H), 7.61-7.53 (m, 2H), 7.52-7.42 (m, 2H), 7.34 (dd, J=8.3, 4.5 Hz, 1H), 2.82 (s, 3H). MS (ESI) m/z 311.1 [M+H]⁺.

EXAMPLE 15 1-(2-Chlorophenyl)-3,5-dimethyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one

To a stirred suspension of sodium hydride (24 mg, 0.10 mmol) in DMF (0.60 mL) is added 1-(2-chlorophenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one (12 mg, 0.039 mmol). After the suspension is stirred at room temperature for 0.5 h, methyl iodide (274 mg, 1.93 mmol) is added. The mixture is stirred at room temperature for 1 h, and then cooled to −70° C. Water (1 mL) is added to quench the reaction, followed by adding DMF (5 mL). The resulting mixture is filtered and the filtrate is isolated with a semi-preparative HPLC system to afford 1-(2-Chlorophenyl)-3,5-dimethyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one (12 mg, 72% yield). ¹H NMR (500 MHz, Chloroform-d) δ 8.22 (dd, J=4.6, 1.2 Hz, 1H), 7.67 (dd, J=8.6, 1.0 Hz, 1H), 7.59-7.53 (m, 2H), 7.51-7.41 (m, 2H), 7.38 (dd, J=8.6, 4.2 Hz, 1H), 3.73 (s, 3H), 2.80 (s, 3H). MS (ESI) m/z 325.1 [M+H]⁺.

EXAMPLE 16 1-(2,5-Dichlorophenyl)-3,5-dimethyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one

The title compound is prepared in an analogous fashion following the procedure described in the synthesis of Example 15 wherein 1-(2,5-dichlorophenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one is added instead of 1-(2-chlorophenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one. ¹H NMR (500 MHz, Chloroform-d) δ 8.27 (dd, J=4.5, 1.4 Hz, 1H), 7.71 (dd, J=8.7, 1.2 Hz, 1H), 7.60 (d, J=2.2 Hz, 1H), 7.53-7.46 (m, 2H), 7.44 (dd, J=8.6, 4.4 Hz, 1H), 3.76 (s, 3H), 2.81 (s, 3H). MS (ESI) m/z 359.0 [M+H]⁺.

EXAMPLE 17 1-(5-Butoxy-2-chlorophenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one

The title compound is prepared in an analogous fashion following the procedure described in the synthesis of Example 13 wherein (5-butoxy-2-chlorophenyl)hydrazine is added instead of 2,5-dichlorophenylhydrazine. MS (ESI) m/z 383.2 [M+H]⁺.

EXAMPLE 18 1-(5-Butoxy-2-fluorophenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one

The title compound is prepared in an analogous fashion following the procedure described in the synthesis of Example 13 wherein (5-butoxy-2-fluorophenyl)hydrazine is added instead of 2,5-dichlorophenylhydrazine. ¹H NMR (500 MHz, Chloroform-d) δ 10.69 (s, 1H), 8.32 (dd, J=4.6, 1.4 Hz, 1H), 7.69 (dd, J=8.4, 1.5 Hz, 1H), 7.37 (dd, J=8.3, 4.5 Hz, 1H), 7.21-7.07 (m, 2H), 7.04-6.96 (m, 1H), 3.98 (t, J=6.5 Hz, 2H), 2.82 (s, 3H), 1.84-1.68 (m, 2H), 1.56-1.42 (m, 2H), 0.97 (t, J=7.4 Hz, 3H). MS (ESI) m/z 367.2 [M+H]⁺.

EXAMPLE 19 8-Chloro-1-(2,5-dichlorophenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one

The title compound is prepared in an analogous fashion following the procedure described in the synthesis of Example 13 wherein 3-acetyl-6-bromo-4-hydroxy-1,5-naphthyridin-2(1H)-one is added instead of 3-acetyl-4-hydroxy-1,5-naphthyridin-2(1H)-one. ¹H NMR (500 MHz, Chloroform-d) δ 10.94 (s, 1H), 7.67 (d, J=8.6 Hz, 1H), 7.58 (d, J=2.3 Hz, 1H), 7.55-7.46 (m, 2H), 7.38 (d, J=8.5 Hz, 1H), 2.81 (s, 3H). MS (ESI) m/z 379.0 [M+H]⁺.

EXAMPLE 20 1-(5-Butoxy-2-chlorophenyl)-8-chloro-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one

The title compound is prepared in an analogous fashion following the procedure described in the synthesis of Example 13 wherein (5-butoxy-2-chlorophenyl)hydrazine and 3-acetyl-6-bromo-4-hydroxy-1,5-naphthyridin-2(1H)-one are added instead of 2,5-dichlorophenylhydrazine and 3-acetyl-4-hydroxy-1,5-naphthyridin-2(1H)-one. ¹H NMR (500 MHz, Chloroform-d) δ 10.83 (s, 1H), 7.66 (d, J=8.6 Hz, 1H), 7.43 (d, J=8.9 Hz, 1H), 7.36 (d, J=8.5 Hz, 1H), 7.09 (d, J=2.9 Hz, 1H), 7.04 (dd, J=8.9, 2.9 Hz, 1H), 3.99 (dt, J=14.3, 7.0 Hz, 2H), 2.81 (s, 3H), 1.91-1.71 (m, 2H), 1.56-1.40 (m, 2H), 0.97 (t, J=7.4 Hz, 3H). MS (ESI) m/z 417.1 [M+H]⁺.

EXAMPLE 21 1-(5-Butoxy-2-chlorophenyl)-8-methoxy-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one

To a solution of 1-(5-butoxy-2-chlorophenyl)-8-chloro-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one (50 mg, 0.12 mmol) in dioxane (2.0 mL) is added sodium methoxide solution (0.5 N, 1 mL in MeOH), followed by adding NaH (60 mg, 2.5 mmol) in portions under argon. The mixture is stirred at room temperature for 10 min and then heated in a sealed tube in a microwave reactor at 160° C. for 6 h. After the reaction mixture is cooled to room temperature, additional sodium methoxide solution (0.5 N, 0.8 mL in MeOH) and NaH (80 mg, 3.3 mmol) are added. The reaction vial is sealed and heated in a microwave reactor at 160° C. for another 6 h. The mixture is cooled to room temperature, quenched with water (100 mL), and then extracted with CH₂Cl₂ (4×25 mL). The combined organic phase is evaporated to dryness under reduced pressure. The obtained residue is purified with a semi-preparative HPLC system using a gradient of 0-70% acetonitrile in water containing 0.1% formic acid over 16 min to give 1-(5-butoxy-2-chlorophenyl)-8-methoxy-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one as an off-white solid (36 mg, 72% yield). ¹H NMR (500 MHz, Chloroform-d) δ 10.82 (s, 1H), 7.65 (d, J=8.8 Hz, 1H), 7.41 (d, J=8.9 Hz, 1H), 7.12 (d, J=2.8 Hz, 1H), 6.98 (dd, J=8.9, 2.8 Hz, 1H), 6.87 (d, J=8.8 Hz, 1H), 4.08-3.88 (m, 2H), 3.36 (s, 3H), 2.82 (s, 3H), 1.83-1.69 (m, 2H), 1.55-1.39 (m, 2H), 0.96 (t, J=7.4 Hz, 3H). MS (ESI) m/z 413.1 [M+H]⁺.

EXAMPLE 22 1-(2-Chloro-5-(cyclobutylmethoxy)phenyl)-8-methoxy-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one

(a) 8-Chloro-1-(2-chloro-5-(cyclobutylmethoxy)phenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one

The title compound is prepared in an analogous fashion following the procedure described in the synthesis of Example 13 wherein (2-chloro-5-(cyclobutylmethoxy)phenyl)hydrazine and 3-acetyl-6-bromo-4-hydroxy-1,5-naphthyridin-2(1H)-one are added instead of 2,5-dichlorophenylhydrazine and 3-acetyl-4-hydroxy-1,5-naphthyridin-2(1H)-one.

(b) 1-(2-Chloro-5-(cyclobutylmethoxy)phenyl)-8-methoxy-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one

To a solution of crude 8-chloro-1-(2-chloro-5-(cyclobutylmethoxy)-phenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one (50 mg, 0.11 mmol) in methanol (1.5 mL) is added sodium methoxide solution (5M, 1 mL in MeOH), followed by adding CuI (22 mg, 0.12 mmol) under argon. The mixture is heated in a sealed tube in a microwave reactor at 130° C. for 1.5 h. The reaction mixture is cooled to room temperature, quenched with water (20 mL), and then extracted with ethyl acetate (20 mL). The combined organic phase is evaporated to dryness under reduced pressure. The obtained residue is purified with a semi-preparative HPLC system using a gradient of 0-43% acetonitrile in water containing 0.1% formic acid over 16 min to give 1-(2-Chloro-5-(cyclobutylmethoxy)phenyl)-8-methoxy-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one as a white solid (14 mg, 30% yield). ¹H NMR (500 MHz, Chloroform-d) δ 10.67 (s, 1H), 7.62 (d, J=8.9 Hz, 1H), 7.41 (d, J=8.9 Hz, 1H), 7.13 (d, J=2.9 Hz, 1H), 6.98 (dd, J=8.9, 2.9 Hz, 1H), 6.86 (d, J=8.9 Hz, 1H), 3.97-3.90 (m, 2H), 3.36 (s, 3H), 2.82 (s, 3H), 2.79-2.72 (m, 1H), 2.16-2.09 (m, 2H), 1.99-1.90 (m, 2H), 1.88-1.81 (m, 2H). MS (ESI) m/z 425.1 [M+H]⁺.

EXAMPLE 23

Measurement of PDE2 Inhibition In Vitro

r-hPDE2A (Accession No. NM_002599, Homo sapiens phosphodiesterase 2A, cGMP-stimulated, transcript variant 1) A mammalian expression cloning vector with recombinant cDNA copy of the gene is purchased from Origene. Protein is expressed via transient transfection of HEK293 cells. The cells are harvested at 48 hours after transfection, washed once with TBS buffer (50 mM Tris-HCl, pH 7.5, 150 mM NaCl), then lysed by sonication in cold homogenization buffer (50 mM Tris-HCl, pH 7.5, 5 mM MgCl₂, 1× protease inhibitor cocktail). The homogenate is centrifuged for 30 min at 15,000 g at 4° C. to obtain the soluble cytosolic fraction. The protein concentration of the cytosol is determined using BCA Protein Assay Kit (Pierce) with bovine serum albumin as a standard.

Assay: PDE2A is assayed with FL-cAMP as substrate. An enzyme titration is first performed to determine the working concentration of PDE. The concentration of the enzyme giving activity of 100 ΔmP in the absence of inhibitor is deemed an appropriate working concentration for PDE.

PDE enzyme is diluted in a standard reaction buffer (10 mM Tris-HCl pH 7.2, 10 mM MgCl₂, 0.1% BSA, 0.05% NaN₃) according to the titration curve. For PDE2 assay the reaction buffer is supplemented with 1 μM cGMP to fully activate the enzyme. 99 μl of diluted enzyme solution is added into each well in a flat bottom 96-well polystyrene plate and then ˜1 μl of test compound dissolved in 100% DMSO is added. The compounds are mixed and pre-incubated with the enzyme for 10 min at room temperature.

The FL-cNMP conversion reaction is initiated by addition of substrate (45 nM final). Enzyme and inhibitor mix (16 μl) and substrate solution (4 μl of 0.225 μM) are combined in a 384-well microtiter plate. The reaction is incubated in the dark at room temperature for 15 min. The reaction is halted by addition of 60 μl of binding reagent (1:400 dilution of IMAP beads in binding buffer supplemented with 1:1800 dilution of antifoam) to each well of the 384-well plate. The plate is incubated at room temperature for 1 hour to allow IMAP binding to proceed to completion, and then placed in an Envision multimode microplate reader (PerkinElmer, Shelton, Conn.) to measure the fluorescence polarization (Δmp).

A decrease in cAMP concentration, measured as decreased Amp, is indicative of inhibition of PDE activity. IC₅₀ values are determined by measuring enzyme activity in the presence of 8 to 16 concentrations of compound ranging from 0.00037 nM to 80,000 nM and then plotting drug concentration versus ΔmP. Test well values are normalized to control reactions run on the same plate (values converted to % of control). IC₅₀ values are estimated using nonlinear regression software, fitting a four-parameter one-site dose-response model (XLFit; IDBS, Cambridge, Mass.). Bottom of curve is fixed at 0% of control.

Quality Controls: To determine the IC₅₀ of an inhibitor, an enzyme concentration that gave optimal signal range of 100-200 milli-polarization units is selected. The total fluorescence intensity of each sample well is measured to calculate the average and standard deviation. If the total fluorescence intensity of any sample well is not within the range of Average±3SD, the mp value of that particular well is discarded.

Using the IMAP procedure described or similarly described above, we screened a proprietary PDE-focused compound library to identify novel compounds with nanomolar PDE2 inhibitory activities. The exemplified compounds of the Disclosure (e.g. compounds of Examples 1-22) are tested and shown to generally have an IC₅₀ value of less than 2 μM, majority of the compounds having an IC₅₀ value of less than or equal to 250 nM, most compounds less than 100 nM, some less than 10 nM. In particular, the IC₅₀ values of Bay 60-7550 and Examples 17, 19, 20, 21 and 22 are shown below.

Example PDE2 IC₅₀ (μM) Bay 60-7550 0.001 19 0.073 20 0.012 17 0.028 21 0.0094 22 0.0059

EXAMPLE 24

Pharmacokinetic Study in Mice

Mice are given a single oral dose of the compound of Example 22 (10 mg/kg, PO) and plasma and brain availability are measured (0.25-4 h) using HPLC and LC-MS using methods analogous to those described in Zhao et al., J. Chromatogr. B. Analyt. Technol. Biomed. Life Sci. (2005) 819(1):73-80 and Appels, N. M., et al., Rapid Commun. Mass Spec. 2005. 19(15): p. 2187-92. The experiment shows that the compound of Example 22 has good brain access as shown in the table below compared to the published standard Bay 60-7550, which has a Cmax of 3 ng/ml; Tmax of 0.25 h and a blood to plasma ratio of 0.04 at 10 mg/kg PO.

PK Ex. 22 10 mg/kg Blood/plasma Parameters Description PO Brain Ratio E Half-life hr 2.4 Cmax (obs) ng/ml 17 1.4 Tmax (obs) hr 2.0 AUC (0-4 hr) ng-hr/ml 50 1.4 (obs area) AUC (area) ng-hr/ml 83 0.9

EXAMPLE 25

Measurements of cGMP in Mouse Brain in vivo:

Mice are given a single intraperitoneal (i.p.) dose of the compound of Example 22 (3 mg/kg) or BAY 60-7550 (3 mg/kg) then killed by focused microwave irradiation of the head 15, 30, or 60 min later, as indicated in FIG. 1. Striatum are dissected from the mouse brains and assayed for levels of cGMP. Trichloroacetic acid (TCA) is added to tissue samples for a final concentration of 5% TCA and the tissue is immediately sonicated in solution and stored on ice. The sonicated sample is centrifuged at 15,000×g for 20 min at 4° C. to remove the precipitated protein. To extract the TCA, the sample is washed three times in water saturated ether. The samples are then dried under vacuum (Speedvac, Savant SPD111V) at room temperature and re-suspended in 100 μL EIA buffer. Both the samples and the cGMP serial diluted standards are acetylated using 0.64 M KOH and 4% acetic anhydride to increase the affinity of the cGMP antibody. Each sample is tested in duplicate in precoated assay plates alongside the 8-point cGMP standard dilutions. In addition, blank, maximum binding (B₀) and non-specific binding wells are included. To all wells containing 50 μL sample or standard, equal volumes of AChE-linked cGMP and cGMP antibody are added. The plate is incubated at 4° C. for 18 hours. The wells are then washed 5 times with wash buffer. Detection reagent containing acetylthiocholine and 2-nitrobenzoic acid is added and the plate is incubated at room temperature until the OD of the B₀ wells is at least 0.5 as recorded by the SoftMax 4.8 software (Molecular Devices, Sunnyvale, Calif.). Each data point is converted to % B/B₀ (100*[(sample or standard OD−average non-specific binding)/(average B₀−average non-specific binding)]). The standards are plotted and fit to a 4-parameter logistic equation (FIG. 1). The concentrations of the samples are interpolated from the standard curve using Microsoft Excel and GraphPad Prizm.

Using the procedure as described or similarly described above, the experiment shows that the compound of Example 22 increases cGMP levels in the striatum of mice after systemic dosing compared to Bay 60-7550 (See FIG. 1), which shows improvement in brain access of the compound of Example 22 compared to Bay60-7550. 

What is claimed is:
 1. A Compound of Formula I

wherein (i) R₁ is C₁₋₄alkyl (ii) R₂ is selected from the group consisting of: H, —OH, halo, C₁₋₄alkyl, C₁₋₄alkoxy, —N(R_(f))(R_(g)), —C(O)N(R_(h))(R_(i)), —C(O)OR_(j), —CN, C₁₋₄alkylthio, heteroaryl, heteroC₃₋₇cycloalkyl or pyrrolidinyl, and aryloxy wherein said aryl is optionally substituted with one or more halo; (iii) R₃ is H or C₁₋₄alkyl; (iv) R_(a), R_(b), R_(c), R_(d) and R_(e) are independently H, halo, —O—C₁₋₆alkyl; (v) R_(f) and R_(g) are independently H, C₁₋₄alkyl or heteroaryl; (vi) R_(h) and R_(i) are independently H or C₁₋₄alkyl; (vii) R_(j) is H or C₁₋₄alkyl; in free or salt form.
 2. The compound according to claim 1, wherein the compound is Formula I(i):

in free or salt form.
 3. The compound according to claim 1, wherein: (i) R₁ is C₁₋₄alkyl; (ii) R₂ is C₁₋₄alkoxy; (iii) R₃ is H; (iv) R_(b) , R_(c) and R_(e) are H; R_(a) is halo and R_(d) is —O—C₁₋₆alkyl; in free or salt form.
 4. The compound according to claim 1, wherein the compound is selected from the group consisting of: 1-(5-Butoxy-2-fluorophenyl)-8-(4-fluorophenoxy)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one; 1-(5-Butoxy-2-fluorophenyl)-8-(dimethylamino)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one; 1-(5-Butoxy-2-fluorophenyl)-3-methyl-8-(pyrrolidin-1-yl)-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one; 1-(5-Butoxy-2-fluorophenyl)-3-methyl-8-(1H-pyrazol-1-yl)-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one; 1-(5-Butoxy-2-fluorophenyl)-3-methyl-8-(pyridin-2-ylamino)-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one; 1-(5-Butoxy-2-fluorophenyl)-8-(ethylthio)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one; 1-(5-Butoxy-2-fluorophenyl)-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carbonitrile; 1-(5-Butoxy-2-fluorophenyl)-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carboxylic acid; Ethyl 1-(5-butoxy-2-fluorophenyl)-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carboxylate; 1-(5-Butoxy-2-fluorophenyl)-N-ethyl-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carboxamide; 1-(5-Butoxy-2-fluorophenyl)-3-methyl-4-oxo-3a,4-dihydro-1H-pyrazolo[4,3-c][1,5]naphthyridine-8-carboxamide; 8-Chloro-1-(2-chloro-5-(cyclopropylmethoxy)phenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one; 1-(2,5-Dichlorophenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one; 1-(2-Chlorophenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one; 1-(2-Chlorophenyl)-3,5-dimethyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one; 1-(2,5-Dichlorophenyl)-3,5-dimethyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one; 1-(5-Butoxy-2-chlorophenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one; 1-(5-Butoxy-2-fluorophenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one; 8-Chloro-1-(2,5-dichlorophenyl)-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one; 1-(5-Butoxy-2-chlorophenyl)-8-chloro-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one; 1-(5-Butoxy-2-chlorophenyl)-8-methoxy-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one; and 1-(2-Chloro-5-(cyclobutylmethoxy)phenyl)-8-methoxy-3-methyl-1H-pyrazolo[4,3-c][1,5]naphthyridin-4(5H)-one; in free or salt form.
 5. A pharmaceutical composition comprising a compound according to claim 1, in combination or association with pharmaceutically acceptable diluents or carrier. 